This proposal focuses on glucocorticoid hormone regulation of the gene encoding glutamine synthetase in the embryonic chick retina. The hormonal induction has been characterized at the levels of enzyme activity and enzyme protein, and therefor represents a well-defined model to examine gene regulation in the developing nervous system. The molecular basis for this steroid hormone action will be investigated through filter hybridization experiments using cloned DNA probes for the glutamine synthetase gene. These studies are intended to establish whether the hormone-mediated rise in glutamine synthetase mRNA has a transcriptional basis and if the hormone initiates a reversible or irreversible alteration in glutamine synthetase gene expression. Subsequent efforts will be directed toward elucidation of the mechanism by which hormonal sensitivity arises exclusively in the Muller glial cells during retina differentiation. Chromatin will be derived from Muller cells, photoreceptor cells, and progenitor neuroepithelial cells and assayed by Southern analysis following nuclease digestions. These experiments are designed to monitor features of chromatin structure that distinguish between transcriptionally active and inactive genes. We intend to establish whether developmental events directed at glutamine synthetase chromatin, result in Muller cell-specific regulation of the gene by the glucocorticoid hormone. Through these studies of glutamine synthetase gene structure and expression, we hope to gain a more general appreciation of the regulatory mechansims involved during embryogenesis of the retina.